Low-redshift Lyman Continuum Survey: Radio continuum properties of low-$z$ Lyman continuum emitters

Abstract

Sources that leak Lyman-continuum (LyC) photons and lead to the reionisation of the universe are intensely studied using multiple observing facilities. Recently, the Low-redshift LyC Survey (LzLCS) has found the first large sample of LyC emitting galaxies at low redshift ($z\sim 0.3$) with the Hubble Space Telescope/Cosmic Origins Spectrograph. The LzLCS sample contains a robust estimate of the LyC escape fraction ($f_{\mathrm{esc}}^{\mathrm{LyC}}$) for 66 galaxies spanning a wide range of $f_{\mathrm{esc}}^{\mathrm{LyC}}$. Here we, for the first time, aim to study the radio continuum (RC) properties of LzLCS sources and their dependence on $f_{\mathrm{esc}}^{\mathrm{LyC}}$. We present Karl G. Jansky Very Large Array RC observations at C (4-8 GHz), S (2-4 GHz) and L (1-2 GHz) bands for a sub-sample of the LzLCS sources. The radio spectral index ($\hat{I}{\pm }_{6GHz}^{3GHz}$) spans a wide range from being flat ( $\ge -0.1$) to very steep ($\le -1.0$). The strongest leakers in our sample show flat $\hat{I}{\pm }_{6GHz}^{3GHz}$, weak leakers have $\hat{I}{\pm }_{6GHz}^{3GHz}$ close to normal star-forming galaxies, and non-leakers are characterized by steep $\hat{I}{\pm }_{6GHz}^{3GHz}$. We argue that a combination of young ages, free-free absorption, and a flat cosmic-ray energy spectrum can altogether lead to a flat $\hat{I}{\pm }_{6GHz}^{3GHz}$ for strong leakers. Non-leakers are characterized by steep spectra which can arise due to break/cutoff at high frequencies. Such a cutoff in the spectrum can arise in a single injection model of CRs characteristic of galaxies which have recently stopped star formation. Such a relation between $\hat{I}{\pm }_{6GHz}^{3GHz}$ and $f_{\mathrm{esc}}^{\mathrm{LyC}}$ hints at the interesting role of supernovae, CRs, and magnetic fields in facilitating the escape ( and/or the lack) of LyC photons. (Abridged)

20 pages, 17 figures, 4 tables, 8 appendix pages, Astronomy & Astrophysics in press